Plasma is a group of charged protons and electrons generated through a discharge, and is being widely used in treating a surface of a substrate in a semiconductor manufacturing process, such as plasma etch and PECVD (Plasma Enhanced-Chemical Vapor Deposition). Nevertheless, the plasma processing method had suffered from a disadvantage that the plasma is a charged particle. For instance, use of charged particles for etching often tends to alter etch profile, damage a circuit formed on the substrate, or lead to voltage gradients which may damage the surface of a substrate.
To overcome such a problem caused by the plasma processing method, systems using neutral particles are suggested. There are two main techniques to produce neutral particles from plasma. One is a charge exchange which produces neutral particles by collisions of the plasma with gas particles. The other is to produce the neutral particles by collisions of the plasma with a heavy metal plate. As an example of the former technique, Japanese patent Nos. 2,606,551 and 2,842,344 may be mentioned as a reference. However, the neutral particles produced through the charge exchange between the plasma and the gas particles had drawbacks that the efficiency of transformation to neutral particles is low and that the directionality of neutral particles and colliding frequency are hard to control. Therefore, the technique to produce neutral particles by collisions of plasma ions with the heavy metal plate is believed to be more desirable.
U.S. Pat. No. 4,662,977 discloses a neutral particle beam processing apparatus for treating a surface of a substrate, comprising a plasma gun which produces plasma and directs the produced plasma to a predetermined direction, and a heavy metal plate which converts plasma ions to neutral particles and redirects the neutral particles to the substrate. The system has an advantage of solving drawbacks of the plasma, but is not suitable for treating the surface of a substrate having a size of 8 inches or more, due to a small cross section of the incident neutral particle beams.
WO 01/84611 filed by the present inventors discloses an apparatus for treating surfaces with neutral particle beams, comprising a high frequency electric power introducing part, a plasma generating part, a neutral particle generating part and a treating part that loads the target substrate. In the apparatus, high frequency electric power is introduced through the high frequency electric power introducing part, gases introduced into the plasma generating part are converted to plasma with the high frequency electric power, the plasma generated inside the plasma generating part are transformed into neutral particles through collisions of the plasma with a heavy metal plate, and the neutral particles thus generated are used to treat the surface of a substrate. An advantage of the neutral particle beam processing apparatus is a generation of uniform plasma that enables to treat targets with comparatively larger areas. Unpublished PCT application, PCT/KR03/02146, discloses a modified neutral particle beam processing apparatus that improves the conversion performance from plasma to neutral particle beams by forming inclined slits or inclined holes within the heavy metal plate to increase the number of plasma collisions to the heavy metal plate, and thereby improving the efficiency of surface treatment of targets. Herein, the inclined slits or inclined holes formed on the heavy metal plate guarantee the collisions of the plasma with the heavy metal plate and prevent plasma and electrons to reach the substrate. The neutral particle beam processing apparatus has advantages that, for example, a plasma discharging space guarantees uniform plasma generation with wider area, and that the effects caused by plasma ions and electrons unconverted to neutral particle is minimized, and that a highly directional neutral particle beams are produced. Nevertheless, according to the neutral particle beam processing apparatus, plasma sheath occurs within the inclined slits or inclined holes and interferes with the production of neutral particles. In other words, the direction of the plasma ions is interrupted by the imperfect sheath formed at the inclined slits or inclined holes and a large number of neutral particles from plasma ions is not reachable to the target.